1. Field of the Invention
The present invention relates generally to a communication control system for ETC (electronic toll collection)-relevant information. More particularly, the invention is concerned with an vehicle-onboard ETC-relevant information communication control apparatus (hereinafter also referred to simply as the vehicle-onboard ETC apparatus) which is mounted on a motor vehicle running on a toll road for exchanging or interchanging through radio wave communication the ETC-relevant information concerning the toll charge/payment and others with ETC communication facility or equipment installed at a toll gate by way of an overhead antenna which may also be termed a toll gate antenna and which is disposed stationarily over and across the toll road and an antenna mounted on a motor vehicle (hereinafter also referred to as the vehicle-mounted antenna) to thereby allow the toll charge/payment settlement processing to be performed on the basis of the ETC-relevant information in a cashless manner.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, description will first be made of a conventional vehicle-onboard ETC-relevant information communication control apparatus known heretofore by reference to FIG. 12 which shows generally and schematically in a block diagram a structure of a hitherto known vehicle-onboard ETC-relevant information communication control apparatus (hereinafter also referred to simply as the vehicle-onboard ETC apparatus) employed in a conventional ETC (electronic toll control) system.
Referring to FIG. 12, the vehicle-onboard ETC apparatus shown in this figure is comprised of a receiving antenna 1R mounted on a motor vehicle for receiving communication signals indicative of toll charge/payment information from an overhead antenna of ETC communication equipment installed at a relevant toll gate station (not shown), a receiving or input amplifier 2 for receiving the communication signal through the medium of the receiving antenna 1R to thereby amplify the communication signal as received, a receiving mixer circuit (which may also be referred to as a down converter) 3 for mixing the received and amplified signal outputted from the input amplifier 2 with an oscillation signal outputted from a local oscillator 3a to thereby generate a communication signal of a frequency lower than that of the received signal, a data demodulator 4 for demodulating the communication signal outputted from the receiving mixer circuit 3 for the purpose of information processing, an electric field intensity detector (hereinafter also referred to simply as the field intensity detector) 5 for detecting the intensity level of the communication signal outputted from the receiving mixer circuit 3 as the electric field intensity level prevailing upon reception of the toll charge/payment-relevant information, a comparator 6 designed for comparing the detected field intensity level with an electric field intensity level set in advance by a controller incorporated in the vehicle-onboard ETC apparatus (which field intensity level will hereinafter be referred to as the preset field intensity or preset field intensity level) to thereby generate as the output an electric field intensity confirmation or discrimination signal when the detected field intensity level is higher than that of the preset field intensity, and a logical product circuit (logical AND circuit) 7 for supplying the communication signal outputted from the data demodulator 4 to the controller 8 of the vehicle-onboard ETC apparatus as the received data when the field intensity discrimination signal mentioned above is outputted from the comparator 6.
Further, the vehicle-onboard ETC-relevant information communication control apparatus is comprised of a low-pass filter 9 for performing a filter processing on data signal to be sent or transmitted to the ETC communication equipment of the toll gate as the communication signal from the controller 8 of the vehicle-onboard ETC apparatus after eliminating high harmonic components, a transmission modulator 10 for modulating a carrier signal outputted from a local oscillator 3a with the transmission signal (i.e., signal for transmission) outputted from the low-pass filter 9, a transmission amplifier 11 for amplifying the modulated transmission data signal outputted from the transmission modulator 10, and a transmitting antenna 1T for sending or transmitting the amplified data signal outputted for transmission from the transmission amplifier 11 to the ETC communication equipment of the toll gate as a communication signal.
In addition, the vehicle-onboard ETC-relevant information communication control apparatus includes a display device 12 for displaying as images the toll charge/payment information and others exchanged or interchanged with the ETC communication equipment installed at the toll gate, an external interface 13 for outputting the toll charge/payment information interchanged with the ETC communication equipment of the toll gate to external equipment of concern (not shown), and an external storage 14 for recording or storing varieties of control information written and to be read by the controller 8 of the vehicle-onboard ETC apparatus.
Now, referring to FIG. 13 showing a communication sequence diagram, description will be directed to operations of the conventional vehicle-onboard ETC-relevant information communication control apparatus implemented in the structure described above.
In the conventional vehicle-onboard ETC-relevant information communication control apparatus or ETC apparatus, the communication signal sent from the ETC communication equipment of a toll gate by way of the overhead antenna thereof (not shown in FIG. 13) is received firstly by the receiving antenna 1R mounted on the motor vehicle to be subsequently amplified by the input amplifier 2, the output of which is then inputted to the receiving mixer circuit 3. The mixer circuit 3 then converts the frequency of the communication signal inputted thereto to a lower frequency (down converting) as mentioned previously. From the output of the receiving mixer circuit 3, the original data before being modulated in the ETC communication equipment of the toll gate is restored through demodulation by means of the data demodulator 4. Further, the field intensity level of the received signal outputted from the mixer circuit 3 is detected by means of the field intensity detector 5. The detected electric field intensity level is compared with the receiving sensitivity discrimination reference level preset by the controller 8 of the vehicle-onboard ETC apparatus by means of the comparator 6. When it is decided by the comparator circuit 6 that the electric field intensity level is higher than the receiving sensitivity discrimination reference level inclusive thereof, then the field intensity discrimination signal is outputted from the comparator circuit 6 to be subsequently supplied to the controller 8 incorporated in the vehicle-onboard ETC apparatus.
Besides, at this time point, the demodulated data outputted from the data demodulator 4 is inputted to the logical product (AND) circuit 7 together with the field intensity discrimination signal. Consequently, so far as the electric field intensity level of the received communication signal is not lower than the receiving sensitivity discrimination reference level preset by the controller 8 of the vehicle-onboard ETC apparatus and thus when the electric field intensity discrimination signal is outputted, the received signal undergone the demodulation is outputted as the received data from the logical product (AND) circuit 7 to be supplied to the controller 8 of the vehicle-onboard ETC apparatus. In response to the input of the field intensity discrimination signal, the controller 8 of the vehicle-onboard ETC apparatus can decide or recognize that the motor vehicle has entered a communication area where radio-wave communication can be carried out between the vehicle-onboard ETC-relevant information communication control apparatus and the ETC communication equipment of the toll gate.
Upon recognition of the entry of the motor vehicle into the communication area by the controller 8 of the vehicle-onboard ETC apparatus, the latter receives a communication signal #1 sent from the ETC information communication equipment of the toll gate, whereupon the controller 8 of the vehicle-onboard ETC apparatus recognizes or determines the carrier frequency for transmission (i.e., transmission frequency) of relevant data from the vehicle-onboard ETC apparatus to the ETC communication equipment. In dependence on the result of the recognition mentioned above, processing of the communication signal #1 is executed. As a result of this processing, the controller 8 of the vehicle-onboard ETC apparatus outputs the transmission data (i.e., data for transmission) to the low-pass filter 9, whereby the carrier signal outputted from the local oscillator 3a is modulated with the transmission data (i.e., data for transmission) by means of the transmission modulator 10. The output signal of the transmission modulator 10 is then amplified by the output amplifier 11 to be subsequently transmitted to the ETC information communication equipment of the toll gate in terms of a communication signal #2 from the transmitting antenna 1T by way of the overhead antenna. In this manner, return or reply communication is started on the side of the vehicle-onboard ETC apparatus (i.e., vehicle-onboard ETC-relevant information communication control apparatus). In succession, exchange or interchange of the communication signals concerning settlement of the ETC charge/payment transaction is performed between the vehicle-onboard ETC apparatus and the ETC communication equipment of the toll gate for a plurality of times (N times) in accordance with the communication protocol established for processing for settlement of the toll charge/payment transaction, whereupon the communication for the toll charge/payment processing between the ETC communication equipment of the toll gate station and the vehicle-onboard ETC apparatus comes to an end.
In the conventional vehicle-onboard ETC-relevant information communication control apparatus or the vehicle-onboard ETC apparatus such as described above, whenever the ETC communication signal of a level not lower than the signal receiving sensitivity of the vehicle-onboard ETC apparatus is received from the ETC communication equipment of the toll gate, the signal carrying the information which complies to the reply request issued by the ETC communication equipment of the toll gate is sent back to the latter regardless of whether or not the vehicle-onboard ETC apparatus is located internally or externally of the communication area and regardless of the environmental conditions for communication.
However, when such situation arises that after the motor vehicle entered a communication-instable area, a lot of time has been taken for the motor vehicle to pass through the communication-instable area due to traffic jam or for any other reasons, error may occur in the reciprocative communication between the ETC communication equipment of the toll gate and the vehicle-onboard ETC apparatus. For coping with such communication error, communication restoring operation (or so-called communication error recovery operation) is performed for a predetermined number of times in an attempt for restoring the communication (i.e., reestablishing the communication path). This operation is also referred to as the retrial operation or simply as the retrial. However, unless the communication is established in the course of such retrial operation, then it is decided that the communication is impossible between the ETC communication equipment installed at the toll gate and the vehicle-onboard ETC apparatus, which thus results in that the communication is ultimately stopped or interrupted, to a disadvantage.
It has empirically been established that the conventional vehicle-onboard ETC-relevant information communication control apparatus (i.e., vehicle-onboard ETC communication apparatus) suffers a problem that the communication error such as mentioned above takes place very frequently in communication-instable areas A and B due to change or variation of the electric field intensity, as is illustrated in FIG. 2. The frequency of occurrence of such communication error increases in the case where a plurality of motor vehicles are forced to run with a short inter-vehicle distance or when the vehicle is forced to run at a low speed or when the motor vehicle is forced to stop or park within the communication-instable area A or B primarily due to the traffic jam. In that case, communication restoring operation is carried out a predetermined number of times in an attempt to restore the normal communication state, as described above. However, when the predetermined number of times preset for the communication restoring retrial operation has been exceeded while failing to restore the normal reciprocative communication between the vehicle-onboard ETC communication apparatus and the ETC communication equipment of the toll gate, it is then decided that the ETC transaction communication is impossible, being accompanied with interruption of the communication between the vehicle-onboard ETC apparatus and the ETC communication equipment installed at the toll gate. Thereafter, any further communication is disabled between the vehicle-onboard ETC apparatus and the ETC control system at any one of the succeeding toll gate stations, to a great disadvantage.
In the light of the state of the art described above, it is an object of the present invention to solve the problems of the conventional ETC control system which is comprised of the vehicle-onboard ETC-relevant information communication control apparatus and ETC communication equipment installed at toll gates of a toll road as described above and to provide an ETC control system of an improved structure which is capable of restricting or limiting the communication between the vehicle-onboard ETC apparatus and the ETC communication equipment of the toll gate during a predetermined time interval until the motor vehicle which entered a communication area has reached a location within the communication area at a current traveling speed where the communication error such as mentioned previously can be avoided.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention an vehicle-onboard ETC-relevant information communication control apparatus mounted on a motor vehicle capable of running on and along a toll road for interchanging information required at least for toll charge/payment transaction with ETC communication equipment of a toll gate installed in association with the toll road to thereby execute toll charge/payment transaction processing on the basis of the ETC-relevant information mentioned above. The vehicle-onboard ETC-relevant information communication control apparatus includes a communication limiting interval setting means for setting a communication limiting interval for disabling function of the vehicle-onboard ETC-relevant information communication control apparatus for conducting communication with the ETC communication equipment of the toll gate until the motor vehicle entered a communication area where communication between the vehicle-onboard ETC-relevant information communication control apparatus and the ETC communication equipment of the toll gate is allowed has traveled for a predetermined distance within the communication area after entry thereto, a vehicle-traveled distance arithmetic means for arithmetically determining a vehicle-traveled distance for which the motor vehicle has traveled within the communication area from a time point when the motor vehicle entered the communication area, and a communication control means for making decision as to whether or not the vehicle-traveled distance arithmetically determined by the vehicle-traveled distance arithmetic means exceeds the communication limiting interval preset by the communication limiting interval setting means, to thereby allow communication between the vehicle-onboard ETC-relevant information communication control apparatus and the ETC communication equipment of the toll gate to be started when the decision is made to such effect that the vehicle-traveled distance has exceeded the communication limiting interval.
In a preferred mode for carrying out the invention, the communication limiting interval setting means may further be so designed as to set the communication limiting interval relatively short when running speed of the motor vehicle is relatively high, while setting the communication limiting interval relatively long when the running speed of the motor vehicle is relatively low.
In another preferred mode for carrying out the invention, the communication limiting interval setting means may be so designed as to set the communication limiting interval by extending in dependence on a traveling speed of the motor vehicle a time period lapsing from a time point when the motor vehicle entered the communication area to a time point at which the ETC-relevant information communication is to be started.
In yet another preferred mode for carrying out the invention, the communication limiting interval setting means may further be so designed as to set the communication limiting interval for disabling communication between the vehicle-onboard ETC-relevant information communication control apparatus and the ETC communication equipment, which interval extends from termination of the communication concerning the toll charge/payment transaction between the ETC communication equipment and the vehicle-onboard ETC-relevant information communication control apparatus to a time point at which any signal can no more be received from the ETC communication equipment for which the communication with the vehicle-onboard ETC-relevant information communication control apparatus has been terminated within the relevant communication area.
By virtue of the structures of the vehicle-onboard ETC-relevant information communication control apparatus according to the present invention which is so arranged as to effectuate the communication limitation after reception of an ETC communication signal, incapability of communication between the ETC communication equipment of a toll gate and the vehicle-onboard ETC apparatus which may be brought about by variation of the electric field intensity occurring under influence of third lobe of an overhead antenna of the ETC communication equipment and reflected radio waves from adjacent motor vehicles can be avoided regardless of temporary stopping of the motor vehicle, running speed thereof and presence of the adjacent motor vehicles, to a great advantage.
Furthermore, with the vehicle-onboard ETC-relevant information communication control apparatus provided by the present invention, the entry of the motor vehicle into the communication area is recognized or confirmed after reception of the communication signal emitted from the overhead antenna of the ETC communication equipment of the toll gate. By virtue of this feature, erroneous recognition of the vehicle position within the communication area due to erroneous recognition of the electric field intensity level as well as erroneous detection thereof can be evaded, whereby it is made possible to impose the communication restriction to the vehicle-onboard ETC apparatus up to a desired position or location within the communication area to thereby realize the ETC-relevant communication between the vehicle-onboard ETC apparatus and the ETC communication equipment installed at the toll gate in an ideal state, to another advantage.
Further, according to the present invention, the distance of the vehicle-onboard ETC apparatus from the overhead antenna of the ETC communication equipment can be recognized or detected with high reliability and accuracy, which can contribute in turn to enhancement of the capability of the vehicle-onboard ETC apparatus for performing communication of the ETC-relevant information with the ETC information communication equipment of the ETC control system, to yet another advantageous effect.
Furthermore, with the vehicle-onboard ETC apparatus according to the present invention, the reply communication limiting interval or period can be changed as a function of the vehicle speed. Owing to this feature, sufficient communication-allowable time period can be ensured regardless of the vehicle speed.
Besides, owing to the feature of the present invention that the communication between the ETC communication equipment of the toll gate and the vehicle-onboard communication apparatus can be interrupted up to a predetermined location after termination of the communication between the vehicle-onboard ETC apparatus and the ETC communication equipment within the communication area. Owing to this feature, even in such traffic situation where a plurality of ETC communication facilities inclusive of the overhead antennas, respectively, are installed in succession on one and the same road or lane in a same direction, the communication disturbance to the succeeding toll gate ETC communication equipment inclusive of the overhead antenna under the influence of the data remaining even after the termination of the communication between the vehicle-onboard ETC apparatus and the preceding ETC communication equipment inclusive of the overhead antenna thereof can be avoided in a satisfactory manner.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.